Correct option is C
Introduction
The distribution (partition) ratio describes how a solute distributes itself between two immiscible solvents at equilibrium.
It equals the ratio of solute concentrations in the two phases and underlies solvent-extraction techniques.
Information Booster
The correct answer is 6. The distribution ratio (K_D) is defined as the concentration of solute in the organic (ether) layer divided by its concentration in the aqueous layer at equilibrium:
K_D = [butyric acid]_ether / [butyric acid]_aqueous
Step 1 — Initial amount of butyric acid: Moles = Molarity × Volume = 0.10 M × 20 mL = 0.10 × (20/1000) L = 2.0 millimole (mmol).
Step 2 — Amount remaining in aqueous layer: Given = 0.5 mmol.
Step 3 — Amount extracted into ether: 2.0 − 0.5 = 1.5 mmol.
Step 4 — Concentrations in each layer:
· Aqueous concentration = 0.5 mmol / 20 mL = 0.025 M
· Ether concentration = 1.5 mmol / 10 mL = 0.15 M
Step 5 — Distribution ratio: K_D = 0.15 / 0.025 = 6.
Thus butyric acid is six times more concentrated in the ether phase than in the aqueous phase.
The key is to use concentrations (accounting for the different volumes of 10 mL ether vs 20 mL water), not the raw amounts.
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